Inheritance of seed weight and lint index related to hereditability of lint percentage in cotton

The data in this paper have been taken from three sets of crosses, viz., the A crosses (Pima X Winesap), the B crosses (Pima X Upright), and the C cross (Winesap X Sea Island). These are three of the four sets of hybrids used in a previous study of lint percentage inheritance. In the former work, the first generation showed lowness of lint percentage to be intensified in the A crosses and completely dominant or slightly intensified in the B crosses. On the other hand, highness of lint percentage was incompletely dominant in the first generation of the C cross. For the purpose of analyzing further the disagreeing features of lint percentage transmission as exhibited in the three sets of crosses, weights of 100 seeds and lint index determinations were taken from plants used in the A, B, and C sets of crosses of the former paper. As in the case with lint percentage, the study for seed weight and the study for lint index are carried through the two sesqui-hybrid generations and the F2 generation of each of the three sets of crosses. The relationship of the F1 generation to its parental strains in seed weight and in lint index was compared with the relationship of the F1 generation to its parental strains in lint percentage. This comparison was made for the three sets of hybrids. It is shown that the low degree of lint percentage in the first generation of the A and B crosses and the intergrade degree of lint percentage in the first generation of the C cross are resultants of intensified seed weight in these conjugate populations and not a definite status of lint amount. The percentage of lint was suppressed, not because of a decrease in lint yield, but by reason of the fact that the seed weight was increased through hybrid vigor. The more true or the more representative measure of lint yield, the weight of lint from 100 seeds, showed that the actual amount of lint in the F1 generation was incompletely dominant in the A and B crosses and slightly intensified or fully dominant in the C cross. A study of the variability of both parental strains and the F1 generation in the three sets of crosses indicates that the parents of the A and B crosses were homozygous for seed weight as well as for lint index, but that the parentage of the C cross, particularly the Sea Island, was not genetically pure for either character. However, the Sea Island parental strain fluctuated much more for lint index than for seed weight. The other (Winesap) parental strain of the C cross also exhibited some more variation in lint index than in seed weight. The F1 seed weight results, likely, were not materially vitiated in the C cross, but whether or not the F1 lint index mean of this cross is just above or just below the Winesap parental strain mean is problematical. The contrasted allelomorphs for seed weight in each of the three sets of crosses were not widely removed from each other, neither were the opposing allelomorphs for lint index, in three hybrid sets, remotely separated. The proximity of the antithetic character pairs for seed weight and also for lint index afforded little opportunity for segregation or for distinct modality in either character. The propinquity of the character pairs, on the other hand, provided good material for studying hybrid vigor transmission from the F1 to generations beyond. Lint index showed no hybrid vigor in the A and B crosses and very little if any in the C cross, consequently, the closeness of the allelomorphic members for this character serve no purpose in tracing the transmission of heterosis. However, with the C cross where lint index appeared to be intensified, the means of this character in the sesqui-hybrid populations and in the F2 population were subtended by some force not present in the A and B crosses. Hybrid vigor as expressed in the seed weight persisted in many of the sesqui-hybrid and F2 plants. The means of these generations occurred at a higher level than would have been maintained without heterosis